The present invention relates to axle assemblies for mounting wheels to vehicles. More particularly, the invention relates to conveniently and securely mounting wheels to bicycles in a manner that allows removal of the wheel without tools.
It has long been known that the quick and easy removal of wheels from bicycles, without the need for tools, has advantages for timely repair of tires and other wheel components and for convenient transport and storage of the entire bicycle. At the same time, a secure and rigid connection of the bicycle wheel is necessary for good handling characteristics and rider safety. A secure connection is most important in the case of the front wheel, since unwanted detachment or instability of the front wheel disproportionately exposes the rider to the risk of a serious accident.
Axle designs that fix a wheel to a bicycle without the need for tools have been popular for many years. In one conventional design, the ends of the wheel axle are displaced perpendicular to the axle's length into slots or “dropouts” in the front fork blades or rear stays of the bicycle. Then the axle is clamped against the faces of the slots in the axial direction by the pressure of a lever-operated cam or screw. Raised tabs or ridges on the faces of the fork blades help to retain the wheel in the slot even if the lever or screw loosens unintentionally. In design variations, other mechanically engaging features are added to the basic design to prevent unintended wheel detachment, ensure a consistent level of clamping force and improve convenience of wheel mounting and dismounting.
Axle systems that secure the axle in slots with clamping force typically provide less stability of the wheel than wheel systems that secure the axle ends in substantially closed bores. Especially where stresses on the bicycle wheel are high, such as in off-road cycling, the advantageous stability of closed bore dropouts have favored “thru-axle” designs. In these designs, a mounting axle is inserted through the fork ends and wheel hub from one side of the bicycle along the axle's length. The axle engages a closed bore in at least one of the fork legs. In more traditional versions of the system, clamps on the ends of the fork legs tightly connect the mounting axle to the fork on either side while an end bolt secures the mounting axle somewhat in the axial direction. Typically, however, such designs do not clamp the fork legs tightly against the hub in the axial direction. Moreover, the dropout bores have narrow slots in order to clamp around the axle by means of screw or cam fasteners. The narrow slots of the dropout bores result in less rigidity under high lateral loads on the wheel than fully closed bores.
The inconvenience of securing multiple clamps has led to the design of “quick release” versions of the thru-axle arrangement. Examples of quick release versions include the devices of U.S. Pat. No. 7,090,308, United States Patent Application Publication Numbers 2009/0072613 and 2009/0140571 and British Patent No. GB2414971B. These devices offer enhanced wheel retention compared to axles that engage open slots. However, with the exception of the first device cited, all these devices stabilize the wheel simply by using the mounting axle to clamp the fork legs against the ends of the hollow axle of the hub.
Regarding the devices cited above, the mounting axles fit tightly in the bore or bores of the fork legs and engage the outboard surfaces of the legs to apply tension in the axial direction to pull the legs inwardly against the hub. However, these devices have no torsionally rigid connection to the legs, which allows torsional flexure to go without resistance. Torsional flexure occurs when a lateral force is applied to the wheel tending to rotate the wheel to the side relative to the handlebars. In this situation, one fork leg tends to move forwardly relative to the other fork leg about the portion of the fork that connects the two fork legs. This pivoting causes the walls defining each leg's apertures (through which the axle extends) to rotate relative to the axle in opposite directions.
This phenomenon is demonstrated by imagining a conventional bicycle wheel secured in a fork with one of the above-referenced devices, and the structures connecting the two fork legs being cut. In a conventional design, the two legs could rotate around the wheel axis independently of one another with relatively little resistance. Although cutting of the structure connecting the forks would rarely be encountered, it is common to encounter torsional forces of the forks against the axle as described above. Therefore, resistance to torque provides advantages.
The quick release thru-axle device disclosed in U.S. Pat. No. 7,090,308 clamps the mounting axle to the fork leg bores when a cam lever is operated by expanding the slotted ends of the hollow mounting axle. Consequently, it provides significant resistance against independent rotational flexure of the legs. Nevertheless, unlike the other devices cited in the previous paragraph, it does not clamp the hub tightly against the fork dropouts in the axial direction.
The need therefore exists for an improved wheel axle system for a bicycle or other vehicle.